Azo dyes for thermotransfer printing

Abstract

Azo dyes useful for thermotransfer printing have the formula ##STR1## where the substituents have the following meanings: X is a radical of the formula IIa or IIb ##STR2## R.sup.1 is H, C.sub.1 -C.sub.6 -alkyl or phenyl which may be substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.2 -alkoxy, chlorine, bromine or cyano,R.sup.2 is H, C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, chlorine or bromine, n is 1 or 2, K is a radical of a coupling component IIH--K III of the aniline, aminonaphthaline, pyrazole, diaminopyridine, hydroxypyridone or tetrahydroquinoline series.

Description

The present invention relates to the use in thermotransfer printing of azo dyes of the formula I ##STR3## where the substituents have the following meanings: X is a radical of the formula IIa or IIb ##STR4## where R.sub.1 is hydrogen, C.sub.1 -C.sub.6 -alkyl, or phenyl which may be substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.2 -alkoxy, chlorine, bromine or cyano,

n is 1 or 2, and R.sup.2 is hydrogen, C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, chlorine or bromine, and K is the radical of a coupling component III H--K III of the aniline, aminonapthaline, pyrazole, diaminopyridine, hydroxypyridone or tetrahydroquinoline series and specifically to a process for transferring these azo dyes by diffusion from a transfer to a plastic-coated substrate with the aid of a thermal printing head.

The technique of thermotransfer printing is common knowledge; suitable heat sources besides lasers and IR lamps are in particular thermal printing heads capable of emitting short heat pulses lasting fractions of a second.

In this preferred embodiment of thermotransfer printing, a transfer sheet which contains the transfer dye together with one or more binders, a support material and possibly further assistants such as release agents or crystallization inhibitors is heated from the back with the thermal printing head, causing the dye to migrate out of the transfer sheet and to diffuse into the surface coating of the substrate, for example into the plastic coat of a coated sheet of paper.

The essential advantage of this process is that the amount of dye to be transferred (and hence the color gradation) can be controlled in a specific manner via the amount of energy supplied to the thermal printing head.

Thermal transfer printing is in general carried out using the three subtractive primaries yellow, magenta and cyan (with or without black), and the dyes used must have the following properties to ensure optimal color recording: ready thermal transferability, little tendency to migrate within or out of the surface coating of the receiving medium at room temperature, high thermal and photochemical stability, and also resistance to moisture and chemicals, no tendency to crystallize on storage of the transfer sheet, a suitable hue for subtractive color mixing, a high molar absorption coefficient, and ready industrial availability.

It is very difficult to meet all these requirements at one and the same time. In particular, the magenta dyes used to date have not been fully satisfactory. This is also true for example of the azo dyes described, and recommended for thermal transfer, in U.S. Pat. No. 4,764,178, which have coupling components based on aniline, tetrahydroquinoline, aminoquinoline or julolidine, and also of the azo dyes known from EP-A-258,856 and U.S. Pat. No. 4,698,651 for the same purpose which have coupling components based on aniline, these dyes differing from the azo dyes I inter alia by the nature of the substituent in the thiazole ring which is ortho to the nitrogen atom.

The azo dyes I themselves are known from earlier German Patent Applications P 38 10 643.4 and P 38 16 698.4 or can be obtained by the methods mentioned therein.

It is an object of the present invention to find suitable red and yellow dyes for thermotransfer printing which come closer to the required property profile than the prior art dyes.

We have found that this object is achieved by the azo dyes I defined at the beginning.

We have also found a process for transferring azo dyes by diffusion from a transfer to a plastic-coated substrate with the aid of a thermal printing head, which comprises using for this purpose a transfer on which are situated one or more of the azo dyes I defined at the beginning.

Suitable alkyl R.sup.1 or R.sup.2 is in particular methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl. Alkyl R.sup.1 may also be pentyl, isopentyl, neopentyl, tert-pentyl, hexyl or 2-methylpentyl.

Alkoxy R.sup.2 is for example methoxy, ethoxy, propoxy, isopropoxy, butoxy or isobutoxy.

Substituted phenyl R.sup.1 is for example methylphenyl, ethylphenyl, methoxyphenyl, ethoxyphenyl, chlorophenyl, bromophenyl or cyanophenyl, in each of which the substituents are in position 2, 3 or 4.

Preferred X of the formula IIa or IIb is for example:

Methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-propoxyethyl, 2-butoxyethyl, 2-pentyloxyethyl, 2-hexyloxyethyl, or 2-, 3- or 4-pyridyl.

Preferred coupling components III are:

aniline derivatives of formula IIIa ##STR5## aminonaphthaline derivatives of the formula IIIb ##STR6## pyrazole derivatives of the formula IIIc ##STR7## diaminopyridine derivatives of the formula IIId ##STR8## hydroxypyridone derivatives of the formula IIIe ##STR9## tetrahydroquinoline derivatives of the formula IIIf ##STR10##

Here the substituents have the following meanings:

R.sup.3, R.sup.3', R.sup.4 and R.sup.4' are each hydrogen; C.sub.1 -C.sub.10 -alkyl whose carbon chain may be interrupted by from one to three oxygen atoms in ether function and which may bear the following substituents: cyano, hydroxyl, phenyl, phenoxy, phenylaminocarbonyloxy, benzyloxy, benzoyloxy, which may have C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, fluorine, chlorine or bromine as substituents, C.sub.1 -C.sub.4 -alkanoyloxy, C.sub.1 -C.sub.6 -alkoxycarbonyloxy, C.sub.1 -C.sub.8 -alkoxycarbonyl, mono- or di-C.sub.1 -C.sub.8 -alkylaminocarbonyloxy, in the last three of which the carbon chain may be interrupted by one or two oxygen atoms in ether function; C.sub.3 -C.sub.5 -alkenyl or C.sub.5 -C.sub.7 -cycloalkyl; phenyl which may be substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -dialkylamino, acetylamino, fluorine, chlorine or bromine; R.sup.5 is hydrogen; chlorine; C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkanoylamino, which may have C.sub.1 -C.sub.4 -alkoxy, phenoxy or chlorine as substituents, C.sub.2 -C.sub.3 -alkenoylamino, benzoylamino, ureido, mono- or di-C.sub.1 -C.sub.4 -alkylureido or C.sub.1 -C.sub.4 -alkylsulfonylamino; R.sup.6 is hydrogen, chlorine, C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkoxy; R.sup.7 is hydrogen, C.sub.1 -C.sub.8 -alkyl or phenyl; R.sup.8 is hydrogen, C.sub.1 -C.sub.8 -alkyl, which may have phenyl, furyl or thienyl as substituents, C.sub.5 -C.sub.7 -cycloalkyl or phenyl.

Suitable alkyl R.sup.3, R.sup.3', R.sup.4, R.sup.4', R.sup.5, R.sup.6, R.sup.7 or R.sup.8 is in particular methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl and tert-butyl.

Alkyls R.sup.3, R.sup.3', R.sup.4, R.sup.4', R.sup.7 and R.sup.8 may each also be for example pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, 2-methylpentyl, heptyl, octyl and 2-ethylhexyl, while R.sup.3, R.sup.3', R.sup.4 and R.sup.4' may each additionally be for example nonyl or decyl.

If the carbon chain of alkyl R.sup.3, R.sup.3', R.sup.4 or R.sup.4' is interrupted by from one to three oxygen atoms, it may be for example: 2-methoxyethyl, 2-ethoxyethyl, 2-propoxyethyl, 2-butoxyethyl, 2- or 3-methoxypropyl, 1-methoxy-2-propyl, 2-ethoxypropyl, 2-propoxypropyl, 4,7-dioxaoctyl, 4,7-dioxanonyl, 4,8-dioxadecyl, 4,7,10-trioxaundecyl or 4,7,10-trioxadodecyl.

Alkyl R.sup.3, R.sup.3', R.sup.4 or R.sup.4' may additionally have cyano and hydroxyl as substituents; corresponding examples are:

cyanomethyl, 2-cyanoethyl and 3-cyanopropyl, 2-hydroxyethyl, 2-hydroxypropyl, 1-hydroxyprop-2-yl, 2-hydroxybutyl, 1-hydroxybut-2-yl, 4-hydroxybutyl and 8-hydroxy-4-oxaoctyl.

Other suitable alkyls R.sup.3, R.sup.3', R.sup.4 and R.sup.4' have phenyl, phenoxy, phenylaminocarbonyloxy and also benzyloxy or benzoyloxy as substituents, for example:

benzyl, 1-phenylethyl, 2-phenylethyl, 2-phenoxyethyl, 6-phenoxy-4-oxahexyl, 2-(phenylaminocarbonyloxy)ethyl,

3-benzyloxypropyl, 2-benzoyloxyethyl, 2-(2-methylbenzoyloxy)ethyl, 2-(4-methylbenzoyloxy)ethyl, 2-(4-chlorobenzoyloxy)ethyl, 2-(4-methoxybenzoyloxy)ethyl, 2-benzoyloxypropyl or 2-benzyloxybutyl.

If alkyl R.sup.3, R.sup.3', R.sup.4 or R.sup.4' is substituted by alkanoyloxy, alkoxycarbonyloxy, alkoxycarbonyl or alkylaminocarbonyloxy, the resulting groups are for example:

2-acetyloxyethyl, 2-propionyloxyethyl, 2-pentanoyloxyethyl, 2-acetyloxypropyl, 3-acetyloxypropyl, 2-propionyloxypropyl, 2-acetyloxybutyl, 4-acetyloxybutyl, 2-propionyloxybutyl and 8-acetyloxy-4-oxaoctyl;

2-(ethoxycarbonyloxy)ethyl, 2-(butoxycarbonyloxy)ethyl and 4-(ethoxycarbonyloxy)butyl;

methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 1-(methoxycarbonyl)ethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 2-(butoxycarbonyl)ethyl, 2-(isobutoxycarbonyl)ethyl, 2-(2-ethylhexyloxycarbonyl)ethyl, 2-(3-oxabutyloxycarbonyl)ethyl, 2-(3-oxapentyloxycarbonyl)ethyl and 2-(3-oxaheptyloxycarbonyl)ethyl;

2-(diethylaminocarbonyloxy)ethyl.

Alkenyl, cycloalkyl or substituted phenyl R.sup.3, R.sup.3', R.sup.4 or R.sup.4' is for example:

allyl or methallyl;

cyclopentyl, cyclohexyl, methylcyclohexyl or cycloheptyl; 2-, 3- or 4-methylphenyl, 2- or 4-methoxyphenyl, 2- or 4-ethoxyphenyl, 4-dimethylaminophenyl, 4-acetylaminophenyl, 5-chlorophenyl or 2,4-dichlorophenyl.

Suitable alkoxy R.sup.5 or R.sup.6 is for example methoxy, ethoxy, propoxy, isopropoxy, butoxy or isobutoxy.

R.sup.5 can also be for example alkanoylamino, alkenoylamino, benzoylamino, alkylureido or alkylsulfonylamino, such as:

acetylamino, propionylamino, methoxyacetylamino, ethoxyacetylamino, chloroacetylamino, phenoxyacetylamino;

acryloylamino or methacryloylamino; N-methylureido, N-butylureido or N,N-dimethylureido; methylsulfonylamino, ethylsulfonylamino, propylsulfonylamino or butylsulfonylamino.

R.sup.8 can also be for example substituted alkyl such as benzyl, 1- or 2-phenylethyl, 2-furylmethyl, 2-(2-furyl)ethyl, 2-(2-thienyl)ethyl or 2-(2-pyridyl)ethyl.

Of the abovementioned coupling components H-K, those of the formulae IIIa, IIIc, IIId, IIIe and IIIf are particularly preferred.

Very particularly preferred coupling components are aniline derivatives IIIa and tetrahydroquinoline derivatives IIIf where the substituents have the following meanings:

R.sup.3 and R.sup.4 are each hydrogen; C.sub.1 -C.sub.8 -alkyl whose carbon chain may be interrupted by an oxygen atom and which may carry cyano, hydroxyl, C.sub.1 -C.sub.4 -alkanoyloxy or C.sub.1 -C.sub.8 -alkoxycarbonyl as substituents; or C.sub.5 -C.sub.7 -cycloalkyl; R.sup.5 is hydrogen, methyl, methoxy or acetylamino; R.sup.6 is hydrogen; and R.sup.7 is methyl.

Preferred azo dyes I may be discerned in the Examples.

The dyes I to be used according to the present invention are notable for the following properties compared with prior art red and blue thermotransfer printing dyes: readier thermal transferability in spite of the higher molecular weight, improved migration properties in the receiving medium at room temperature, higher thermal stability, higher lightfastness, better resistance to moisture and chemicals, better solubility in printing ink preparation, higher color strength, and readier industrial accessability.

In addition, the azo dyes I exhibit a distinctly better purity of hue, in particular in mixtures of dyes, and produce improved black prints.

The transfer sheets required as dye donors for the thermotransfer printing process according to the present invention are prepared as follows. The azo dyes I are incorporated in an organic solvent, such as isobutanol, methyl ethyl ketone, methylene chloride, chlorobenzene, toluene, tetrahydrofuran or a mixture thereof, together with one or more binders and possibly further assistants such as release agents or crystallization inhibitors to form a printing ink in which the dyes are preferably present in a molecularly dispersed, ie. dissolved, form. The printing ink is then applied to an inert support and dried.

Suitable binders for the use of the azo dyes I according to the present invention are all materials which are soluble in organic solvents and which are known to be suitable for thermotransfer printing, eg. cellulose derivatives such as methylcellulose, hydroxypropylcellulose, cellulose acetate or cellulose acetobutyrate, but in particular ethylcellulose and ethylhydroxyethylcellulose, starch, alginates, alkyd resins and vinyl resins such as polyvinyl alcohol or polyvinylpyrrolidone but in particular polyvinyl acetate and polyvinyl butyrate. It is also possible to use polymers and copolymers of acrylates and derivatives thereof, such as polyacrylic acid, polymethyl methacrylate or styrene/acrylate copolymers, polyester resins, polyamide resins, polyurethane resins or natural resins such as gum arabic.

It is frequently advisable to use mixtures of these binders, for example mixtures of ethylcellulose and polyvinyl butyrate in a weight ratio of 2 : 1.

The weight ratio of binder to dye is in general from 8 : 1 to 1 : 1, preferably from 5 : 1 to 2 : 1.

Suitable assistants are for example release agents based on perfluorinated alkylsulfonamidoalkyl esters or silicones as described in EP-A-227,092 and EP-A-192,435, and in particular organic additives which stop the transfer dyes from crystallizing out in the course of storage or heating of the inked ribbon, for example cholesterol or vanillin.

Inert support materials are for example tissue, blotting or parchment paper and films made of heat resistant plastics such as polyesters, polyamides or polyimides, which films may also be metal coated.

The inert support may additionally be coated on the side facing the thermal printing head with a lubricant in order that adhesion of the thermal printing head to the support material may be prevented. Suitable lubricants are for example silicones or polyurethanes as described in EP-A-216,483.

The thickness of the support is in general from 3 to 30 .mu.m, preferably from 5 to 10 .mu.m.

The substrate to be printed, eg. paper, must in turn be coated with a binder which receives the dye during the printing process. It is preferable to use for this purpose polymeric materials whose glass transition temperatures T.sub.g are within the range from 50.degree. to 100.degree. C., eg. polycarbonates and polyesters. Details may be found in EP-A-227,094, EP-A-133,012, EP-A-133,011, JP-A-199,997/1986 or JP-A-283,595/1986.

The process according to the present invention is carried out using a thermal printing head which is heatable to above 300.degree. C., so that dye transfer takes not more than 15 msec.

EXAMPLES

First, transfer sheets (donors) were produced in a conventional manner from a polyester sheet 8 .mu.m in thickness coated with an approximately 5 .mu.m thick transfer layer of a binder B which in each case contained about 0.25 g of azo dye I. The weight ratio of binder to dye was in each case 4 : 1.

The substrate (receiver) to be printed was paper about 120 .mu.m in thickness which had been coated with a layer of plastic 8 .mu.m in thickness (Hitachi Color Video Print Paper).

Donor and receiver were placed on top of one another with the coated fronts next to each other then wrapped in aluminum foil and heated between two hotplates at 70.degree.-80.degree. C. for 2 minutes. This operation was repeated three times with similar samples at a temperature within the range from 80.degree. to 120.degree. C., the temperature being increased each time.

The amount of dye diffusing into the plastics layer of the receiver in the course of transfer is proportional to the optical density determined photometrically as absorbance A after each heating phase at the abovementioned temperatures.

The plot of the logarithm of the measured absorbances A against the corresponding reciprocal of the absolute temperature is a straight line from whose slope it is possible to calculate the activation energy .DELTA.E.sub.T for the transfer experiment: ##EQU1##

From the plot it is additionally possible to discern the temperature T* at which the absorbance attains the value 2, ie. at which the transmitted light intensity is one hundredth of the incident light intensity. The lower the temperature T*, the better the thermal transferability of the particular dye.

Tables la to 9a list the azo dyes I which were studied in respect of their thermal transfer characteristics together with their hues.

The related Tables 1b to 9b list the particular binder B used employing the following abbreviations: EC=ethylcellulose, PVB=polyvinyl butyrate, MIX=EC:PVB=2:1, EHEC=ethylhydroxyethylcellulose, CA=cellulose acetate) and the previously mentioned parameters T* [.degree.C.]and .DELTA.E.sub.T [kcal/mol].

TABLE 1a__________________________________________________________________________ ##STR11## IIIaEx. R.sup.1 n R.sup.3 R.sup.4 R.sup.5 R.sup.6 Hue__________________________________________________________________________ 1 CH.sub.3 2 C.sub.4 H.sub.9 CH(CH.sub.3)C.sub.2 H.sub.5 NHCOCH.sub.3 H violet 2 CH.sub.3 2 C.sub.3 H.sub.7 C.sub.3 H.sub.7 NHCOCH.sub.3 H violet 3 CH.sub.3 2 C.sub.6 H.sub.13 C.sub.2 H.sub.5 OCH.sub.3 H violet 4 CH.sub.3 2 H C.sub.4 H.sub.9 CH.sub.3 OCH.sub.3 violet 5 CH.sub.3 2 C.sub.2 H.sub.5 C.sub.2 H.sub.5 H H violet 6 CH.sub.3 2 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.2 OCH.sub.3 H H violet 7 CH.sub.3 2 (CH.sub.2).sub.2 OCOCH.sub.3 (CH.sub.2).sub.2 OCOCH.sub.3 CH.sub.3 H bluish red 8 CH.sub.3 2 (CH.sub.2).sub.2 Ph (CH.sub.2).sub.2 CN H H red 9 CH.sub.3 2 (CH.sub.2).sub.2 OCOC.sub.2 H.sub.5 (CH.sub.2).sub.2 OCOC.sub.2 H.sub.5 Cl H red10 CH.sub.3 2 (CH.sub.2).sub.2 OCOC.sub.2 H.sub.5 (CH.sub.2).sub.2 CN H H red11 CH.sub.3 2 (CH.sub.2).sub.2 CN (CH.sub.2 CHCH.sub.2 H H red12 CH.sub.3 2 (CH.sub.2).sub.2 OCOCH.sub.3 (CH.sub.2).sub. 2 OCOCH.sub.3 CH.sub.3 OCH.sub.3 violet13 CH.sub.3 2 CH.sub.2 CHCH.sub.2 CH.sub.2 CHCH.sub.2 NHCOCH.sub.3 OCH.sub.3 reddish blue14 CH.sub.3 2 (CH.sub.2).sub.2 COO(CH.sub.2).sub.2 OC.sub.2 H.sub.5 C.sub.2 H.sub.5 H H red15 CH.sub.3 2 (CH.sub.2).sub.2 CN C.sub.2 H.sub.5 CH.sub.3 H bluish red16 CH.sub.3 2 (CH.sub.2).sub.2 COOCH.sub.3 C.sub.2 H.sub.5 H H red17 CH.sub.3 2 (CH.sub.2).sub.2 OH C.sub.4 H.sub.9 CH.sub.3 H violet18 CH.sub.3 2 C.sub.2 H.sub.5 C.sub.2 H.sub.5 NHCOCH.sub.3 H violet19 CH.sub.3 2 (CH.sub.2).sub.2 OCOCH.sub.3 C.sub.2 H.sub.5 CH.sub.3 H violet20 CH.sub.3 2 (CH.sub.2).sub.2 OCOCH.sub.3 (CH.sub.2).sub.2 OCOCH.sub.3 H H red21 C.sub.2 H.sub.5 2 (CH.sub.2).sub.2 CN C.sub.2 H.sub.5 CH.sub.3 H bluish red22 C.sub.2 H.sub.5 2 CH.sub.2Ph (CH.sub.2).sub.2 COOCH.sub.3 H H red23 C.sub.2 H.sub.5 2 C.sub.2 H.sub.5 C.sub.2 H.sub.5 H H violet24 C.sub.4 H.sub.9 2 C.sub.2 H.sub.5 C.sub.2 H.sub.5 H H red25 CH.sub.3 1 (CH.sub.2).sub.2 CN C.sub.2 H.sub.5 CH.sub.3 H bluish red26 CH.sub.3 1 (CH.sub.2).sub.2 COOCH.sub.3 C.sub.2 H.sub.5 H H red27 CH.sub.3 1 (CH.sub.2).sub.2 OH C.sub.4 H.sub.9 CH.sub.3 H violet28 C.sub.4 H.sub.9 2 C.sub.2 H.sub.5 C.sub.2 H.sub.5 NHCOCH.sub.3 H violet29 C.sub.4 H.sub.9 2 (CH.sub.2).sub.2 OCOCH.sub.3 C.sub.2 H.sub.5 CH.sub.3 H violet30 C.sub.4 H.sub.9 2 (CH.sub.2).sub.2 OCOCH.sub.3 (CH.sub.2)OCOCH.sub.3 H H red31 C.sub.4 H.sub.9 2 C.sub.4 H.sub.9 (CH.sub.2).sub.2 CN H H red32 C.sub.4 H.sub.9 2 CH.sub.2Ph (CH.sub.2).sub.2 COOC.sub.4 H.sub.9 H H red__________________________________________________________________________ TABLE 2a______________________________________ ##STR12## IIIcEx. R.sup.1 R.sup.7 R.sup.8 Hue______________________________________33 CH.sub.3 H Cyclohexyl yellowish orange34 CH.sub.3 H Ph yellowish orange35 CH.sub.3 H Fur-2-ylmethyl yellowish orange36 CH.sub.3 CH.sub.3 Ph yellowish orange37 C.sub.2 H.sub.5 H CH.sub.2Ph yellowish orange38 C.sub.2 H.sub.5 H Cyclohexyl yellowish orange39 C.sub.4 H.sub.9 H Cyclohexyl yellowish orange40 C.sub.4 H.sub.9 H Ph yellowish orange41 C.sub.4 H.sub.9 CH.sub.3 Fur-2-ylmethyl yellowish orange______________________________________ TABLE 3a ##STR13## IIId Ex. R.sup.1 n R.sup.3 ' R.sup.3 R.sup.4 Hue 42 CH.sub.3 2 H H (CH.sub.2).sub.3O(CH.sub.2).sub.2OCH.sub.3 reddish orange 43 C.sub.2 H.sub.5 2 H H (CH.sub.2).sub.3O(CH.sub.2).sub.2OC.sub.2 H.sub.5 reddish orange 44 CH.sub.3 2 H H (CH.sub.2).sub.3O[(CH.sub.2).sub.2O].sub.2C.sub. 2 H.sub.5 reddish orange 45 CH.sub.3 2 H H (CH.sub.2).sub. 3O(CH.sub.2).su b.4OCOCH.sub.3 reddish orange 46 CH.sub.3 2 (CH.sub.2).sub.3 OCH.sub.3 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.2OCH.sub.3 red 47 CH.sub.3 2 CH(C.sub.2 H.sub.5)CH.sub.2 OCOCH.sub.3 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.2OCH.sub.3 red 48 CH.sub.3 2 (CH.sub.2).sub.3 OCH.sub.3 (CH.sub.2).sub.2 OCOCH.sub.3 C.sub.2 H.sub.5 red 49 C.sub.2 H.sub.5 2 (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OCH.sub.3 H H reddish orange 50 CH.sub.3 2 (CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 C.sub.2 H.sub.5 H H reddish orange 51 CH.sub.3 2 (CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 C.sub.2 H.sub.5 (CH.sub.2).sub. 3 OCH.sub.3 H red 52 CH.sub.3 2 ( CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 CH.sub.3 Ph H pink 53 CH.sub.3 2 (CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 CH.sub.3 Ph-2-OCH.sub.3 H pink 54 CH.sub.3 2 C.sub.2 H.sub.5 (CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 CH.sub.3 H red 55 CH.sub.3 2 C.sub.2 H.sub.5 ( CH.sub.2).sub.3 O(CH.sub.2).sub.4 OH H red 56 C.sub.4 H.sub.9 2 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.3 O(CH.sub.2).sub.4 O H H red 57 CH.sub.3 2 (CH.sub.2).sub.3 OCH.sub.3 (CH.sub.2).sub.3 O(CH.sub.2).sub.4 OH H red 58 CH.sub.3 2 (CH.sub.2).sub.3 O COCH.sub.3 (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OC.sub.2 H.sub.5 H red 59 CH.sub.3 2 C.sub.2 H.sub.5 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.2OCH.sub.3 red 60 CH.sub.3 2 (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OCH.sub.3 Ph-2-OCH.sub.3 H red 61 CH.sub.3 2 (CH.sub.2).sub.2 OCH.sub.3 ( CH.sub.2).sub.2 OCH.sub.3 H red 62 C.sub.2 O( H.sub.5 2 H H (CH.sub.2).sub.3CH.sub.2).sub.2OCH.sub.3 reddish orange 63 CH.sub.3 1 H H (CH.sub.2).sub.3O(CH.sub.2).sub.2OC.sub.2 H.sub.5 reddish orange 64 C.sub.4 H.sub.9 2 H H (CH.sub.2).sub.3O](CH.sub.2).sub.2O].sub.2C.sub.2 H.sub.5 reddish orange 65 C.sub.3 H.sub.7 2 H H (CH.sub. 2).sub.3O(CH.sub.2).sub.4OCOCH.sub.3 reddish orange 66 C.sub.2 H.sub.5 1 (CH.sub.2).sub.3 OCH.sub.3 (CH.sub.2).sub.2 C OH.sub.3 (CH.sub.2).sub.2OCH.sub.3 red 67 CH.sub.3 1 CH(C.sub.2 H.sub.5)CH.sub.2 OCOCH.sub.3 (CH.sub.2).sub.2 OC OCH.sub.3 (CH.sub.2).sub.2H.sub.3 red 68 C.sub.4 H.sub.9 2 (CH.sub.2).sub.3 OCH.sub.3 (CH.sub.2).sub.2 OCOCH.sub.3 C.sub.2 H.sub.5 red 69 C.sub.4 H.sub.9 2 (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OPh (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.2OCH.sub.3 red TABLE 4a______________________________________ ##STR14## IIIeEx. R.sup.1 R.sup.3 Hue______________________________________70 CH.sub.3 C.sub.2 H.sub.5 yellow71 CH.sub.3 C.sub.4 H.sub.9 yellow72 CH.sub.3 (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OPh yellow______________________________________ TABLE 5a__________________________________________________________________________ ##STR15## IIIfEx. R.sup.1 n R.sup.3 R.sup.5 Hue__________________________________________________________________________73 CH.sub.3 2 C.sub.2 H.sub.5 H violet74 C.sub.2 H.sub.5 2 C.sub.3 H.sub.7 H violet75 CH.sub.3 2 C.sub.4 H.sub.9 CH.sub.3 violet76 CH.sub.3 2 (CH.sub.2).sub.2 OC.sub.4 H.sub.9 NHCOCH.sub.3 violet77 C.sub.4 H.sub.9 1 C.sub.2 H.sub.5 CH.sub.3 violet78 CH.sub.3 2 (CH.sub.2).sub.2 OCH.sub.3 H violet79 C.sub.4 H.sub.9 2 C.sub.2 H.sub. 5 H violet80 CH.sub.3 2 H H bluish red81 C.sub.6 H.sub.13 2 C.sub.4 H.sub.9 CH.sub.3 violet82 CH.sub.3 2 (CH.sub.2).sub.2 COOCH.sub.2 OH CH.sub.3 violet83 C.sub.2 H.sub.5 1 (CH.sub.2).sub.2 CN NHCOCH.sub.3 violet84 CH.sub.3 1 CH.sub.2 O(CH.sub.2).sub.2 OPh NHCOCH.sub.3 violet85 CH.sub.3 1 C.sub.2 H.sub.5 NHSOOC.sub.4 H.sub.9 violet86 C.sub.2 H.sub.5 2 (CH.sub.2).sub.2 OCOC.sub.6 H.sub.13 NHSOOC.sub.2 H.sub.5 violet87 CH.sub.3 1 (CH.sub.2).sub.2 OCOC.sub.3 H.sub.7 NHCOC.sub.4 H.sub.9 violet__________________________________________________________________________ TABLE 6a__________________________________________________________________________ ##STR16## IIIa Position ofEx. pyridyl group R.sup.3 R.sup.4 R.sup.5 R.sup.6 Hue__________________________________________________________________________88 3 (CH.sub.2).sub.2 CN C.sub.2 H.sub.5 CH.sub.3 H red89 3 (CH.sub.2).sub.2 COOCH.sub.3 C.sub.2 H.sub.5 H H red90 3 (CH.sub.2).sub.2 OH C.sub.4 H.sub.9 CH.sub.3 H red91 3 C.sub.2 H.sub.5 C.sub.2 H.sub.5 NHCOCH.sub.3 H pink92 3 (CH.sub.2).sub.2 OCOCH.sub.3 C.sub.2 H.sub.5 CH.sub.3 H red93 3 (CH.sub.2).sub.2 OCOCH.sub.3 (CH.sub.2).sub.2 OCOCH.sub.3 H H red94 3 C.sub.2 H.sub.5 C.sub.2 H.sub.5 H H red95 3 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.2 OCH.sub.3 H H red96 3 (CH.sub.2).sub.2 OCOCH.sub.3 (CH.sub.2).sub.2 OCOCH.sub.3 CH.sub.3 H red97 3 (CH.sub.2).sub.2Ph (CH.sub.2).sub.2 CN H H red98 3 (CH.sub.2).sub.2 OCOC.sub.2 H.sub.5 (CH.sub.2).sub.2 OC.sub.2 H.sub.5 Cl H red99 3 (CH.sub.2).sub.2 OCOC.sub.2 H.sub.5 (CH.sub.2).sub.2 CN H H red100 3 (CH.sub.2).sub.2 CN CH.sub.2 CHCH.sub.2 H H red101 3 (CH.sub.2).sub.2 OCOCH.sub.3 (CH.sub.2).sub.2 OCOCH.sub.3 CH.sub.3 OCH.sub.3 violet102 3 CH.sub.2 CHCH.sub.2 CH.sub.2 CHCH.sub.2 NHCOCH.sub.3 OCH.sub.3 bluish violet103 3 (CH.sub.2).sub.2 COO(CH.sub.2).sub.2 OC.sub.2 H.sub.5 C.sub.2 H.sub.5 H H red104 4 (CH.sub.2).sub.2 CN C.sub.2 H.sub.5 CH.sub.3 H red105 4 CH.sub.2Ph (CH.sub.2).sub.2 COOCH.sub.3 H H red106 4 C.sub.2 H.sub.5 C.sub.2 H.sub.5 H H red107 2 (CH.sub.2).sub.2 CN C.sub.2 H.sub.5 H H red__________________________________________________________________________ TABLE 7a______________________________________ ##STR17## IIIc Position ofEx. pyridyl group R.sup.8 Hue______________________________________108 3 Cyclohexyl yellowish orange109 3 Ph yellowish orange110 3 Fur-2-ylmethyl yellowish orange111 4 Ph yellowish orange112 4 CH.sub.2Ph yellowish orange______________________________________ TABLE 8a__________________________________________________________________________ ##STR18## IIIdEx. R.sup.3' R.sup.3 R.sup.4 Hue__________________________________________________________________________113 H H (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OCH.sub.3 reddish orange114 H H (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OC.sub.2 H.sub.5 reddish orange115 H H (CH.sub.2).sub.3 O[(CH.sub.2).sub. 2 O].sub.2 C.sub.2 H.sub.5 reddish orange116 H H (CH.sub.2).sub.3 O(CH.sub.2).sub.4 O COCH.sub.3 reddish orange117 (CH.sub.2).sub.3 OCH.sub.3 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.2 OCH.sub.3 red118 CH(C.sub.2 H.sub.5)CH.sub.2 OCOCH.sub.3 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.2 OCH.sub.3 red119 (CH.sub.2).sub.3 OCH.sub.3 (CH.sub.2).sub.2 OCOCH.sub.3 C.sub.2 H.sub.5 red120 (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OCH.sub.3 H H reddish orange121 (CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 C.sub.2 H.sub.5 H H reddish orange122 (CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 C.sub.2 H.sub.5 (CH.sub.2).sub.3 OCH.sub.3 H red123 (CH.sub.2).sub.3 O[(CH.sub.2 ).sub.2 O].sub.2 CH.sub.3 Ph H red124 (CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 CH.sub.3 Ph-2-OCH.sub.3 H red125 C.sub.2 H.sub.5 (CH.sub.2).sub.3 O[(CH.sub.2).sub.2 O].sub.2 CH.sub.3 C.sub.4 H.sub.9 pink126 C.sub.2 H.sub.5 (CH.sub.2).sub.3 O(CH.sub.2).sub.4 OH H red127 (CH.sub.2).sub.2 OCH.sub.3 (CH.sub.2).sub.3 O(CH.sub.2).sub.4 OH C.sub.2 H.sub.5 pink128 (CH.sub.2).sub.3 OCH.sub.3 (CH.sub.2).sub.3 O(CH.sub.2).sub.4 OH H red129 (CH.sub.2).sub.3 OCOCH.sub.3 (CH.sub.2).sub.3 O(CH.sub.2).sub.2 OC.sub.2 H.sub.5 red__________________________________________________________________________ TABLE 9a__________________________________________________________________________ ##STR19##Ex. Position of pyridyl group R.sup.3 R.sup.5 Hue__________________________________________________________________________130 3 C.sub.3 H.sub.7 H violet131 3 C.sub.2 H.sub.5 CH.sub.3 violet132 3 C.sub.4 H.sub.9 NHCOCH.sub.3 violet133 3 (CH.sub.2).sub.2 OC.sub.4 H.sub.9 NHCOCH.sub.3 violet134 2 C.sub.6 H.sub.13 CH.sub.3 violet135 3 (CH.sub.2).sub.2 COOC.sub.7 H.sub.15 NHCOCH.sub.3 violet136 3 (CH.sub.2).sub.2 OCOC.sub.6 H.sub.13 NHCOCH.sub.3 violet137 3 (CH.sub.2).sub.4 CH(CH.sub.3)C.sub.2 H.sub.5 CH.sub.3 violet138 3 C.sub.3 H.sub.7 OCH.sub.3 violet139 3 [(CH.sub.2).sub.2 O].sub.2 C.sub.4 H.sub.9 NHCOCH.sub.3 violet140 3 (CH.sub.2).sub.4 OH NHCOCH.sub.3 violet141 3 (CH.sub.2).sub.2 OH CH.sub.3 violet142 2 (CH.sub.2).sub.2 CN NHCOC.sub.4 H.sub.9 violet143 3 C.sub.4 H.sub.9 H violet144 3 C.sub.7 H.sub.15 H violet145 3 H H violet146 2 H CH.sub.3 violet147 3 H C.sub.2 H.sub.5 violet__________________________________________________________________________ TABLE 1b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 1a Example B T*[.degree.C.] ##STR20##______________________________________ 1 EC 82 16 2 EC 93 14 3 EC 100 15 4 EC 90 17 5 EC 80 16 6 EC 82 17 7 EC 86 17 8 EC 89 19 9 EC 80 2310 EC 90 1611 EC 98 1512 EHE 96 1913 CA 100 1914 EC 102 2115 EHE 98 1916 EC 91 1817 EC 93 2018 EC 95 1619 EC 92 1720 EC 95 1621 CA 93 1222 MIX 96 1323 MIX 97 1524 MIX 101 1725 MIX 99 1926 MIX 88 1827 MIX 91 1928 MIX 93 1729 MIX 85 1930 MIX 94 1831 EC 90 1632 EHE 90 20______________________________________ TABLE 2b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 2a Example B T*[.degree.C.] ##STR21##______________________________________33 MIX 97 1334 EHE 88 1735 CA 99 1636 MIX 99 1937 MIX 99 1938 MIX 89 2139 MIX 88 1940 MIX 99 1741 MIX 86 16______________________________________ TABLE 3b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 3a Example B T*[.degree.C.] ##STR22##______________________________________42 EC 106 1643 EC 98 1744 EHE 80 2045 CA 94 1946 EC 93 1147 EC 82 1248 EC 91 1649 EC 98 1750 EC 85 1851 EC 99 1952 EC 96 1753 MIX 97 1954 MIX 93 1855 MIX 100 1956 MIX 100 1857 MIX 99 1958 MIX 89 1359 EC 99 1960 EC 88 1961 MIX 99 2062 EC 86 1663 EHE 94 2264 MIX 83 1465 MIX 104 2066 MIX 99 1767 MIX 79 2068 EC 99 1369 EC 88 2______________________________________ TABLE 4b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 4a Example B T*[.degree.C.] ##STR23##______________________________________70 EC 93 1771 MIX 99 1572 MIX 88 12______________________________________ TABLE 5b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 5a Example B T*[.degree.C.] ##STR24##______________________________________73 MIX 97 2174 MIX 95 1975 EC 96 1876 EHE 93 1777 MIX 110 1678 MIX 99 1579 EC 106 2080 MIX 99 2181 CA 98 2282 MIX 96 1983 MIX 84 2284 EC 94 1385 EHE 90 1486 MIX 99 1787 EC 99 16______________________________________ TABLE 6b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 6a Example B T*[.degree.C.] ##STR25##______________________________________ 88 MIX 89 16 89 MIX 89 20 90 MIX 99 19 91 MIX 98 20 92 MIX 99 19 93 MIX 96 18 94 MIX 99 22 95 MIX 98 19 96 MIX 80 18 97 MIX 99 22 98 MIX 89 19 99 MIX 99 18100 MIX 109 17101 MIX 107 16102 MIX 96 21103 MIX 89 19104 MIX 98 18105 MIX 84 17106 MIX 94 19107 MIX 95 14______________________________________ TABLE 7b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 7a Example B T*[.degree.C.] ##STR26##______________________________________108 MIX 98 15109 MIX 97 19110 MIX 96 21111 MIX 95 17112 MIX 93 19______________________________________ TABLE 8b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 8a Example B T*[.degree.C.] ##STR27##______________________________________113 MIX 99 17114 MIX 99 16115 MIX 89 19116 MIX 97 19117 MIX 86 18118 MIX 99 17119 MIX 98 16120 MIX 95 15121 MIX 97 19122 MIX 96 18123 MIX 99 14124 MIX 98 19125 MIX 85 13126 MIX 101 19127 MIX 98 18128 MIX 87 17129 MIX 96 20______________________________________ TABLE 9b______________________________________THERMOTRANSFER DATA RELATING TO TABLE 9a Example B T*[.degree.C.] ##STR28##______________________________________130 EC 88 15131 MIX 97 16132 MIX 97 17133 MIX 96 19134 EC 98 17135 EC 89 22136 EHE 95 17137 MIX 104 18138 MIX 98 19139 MIX 89 18140 MIX 97 16141 MIX 96 13142 MIX 95 14143 MIX 92 17144 MIX 90 18145 MIX 111 19146 MIX 89 18147 MIX 98 19______________________________________

Claims

1. A process for transferring an azo dye by diffusion from a transfer to a plastic-coated substrate with the aid of a heat source, which comprises using for this purpose a transfer on which there is or are situated one or more azo dyes of the formula I ##STR29## in which the substituents have the following meanings: X is a radical of the formula IIa or IIb ##STR30## where R.sup.1 is hydrogen, C.sub.1 -C.sub.6 -alkyl, or phenyl which may be substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.2 -alkoxy, chlorine, bromine or cyano,

n is 1 or 2, and

R.sup.2 is hydrogen, C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, chlorine or bromine, and

K is the radical of a coupling component III

H--K III

of an aniline, aminoaphthaline, pyrazole, hydroxypyridone or tetrahydroquinoline.

2. A process as claimed in claim 1, wherein K is of:

aniline derivatives of formula IIIa ##STR31## aminoaphthaline derivatives of the formula IIIb ##STR32## pyrazole derivatives of the formula IIIc ##STR33## hydroxypyridone derivatives of the formula IIIe ##STR34## tetrahydroquinoline derivatives of the formula IIIf ##STR35## wherein R.sup.3 and R.sup.4 are each hydrogen; C.sub.1 -C.sub.10 -alkyl whose carbon chain may be interrupted by from one to three oxygen atoms in ether function and which may bear the following substituents: cyano, hydroxyl, phenyl, phenoxy, phenylaminocarbonyloxy, benzyloxy, benzoyloxy, which may have C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, fluorine, chlorine or bromine as substituents, C.sub.1 -C.sub.4 -alkanoyloxy, C.sub.1 -C.sub.6 -alkoxycarbonyloxy, C.sub.1 -C.sub.8 -alkoxycarbonyl, mono- or di-C.sub.1 -C.sub.8 -alkylaminocarbonyloxy, in the last three of which the carbon chain may be interrupted by one or two oxygen atoms in ether function;

C.sub.3 -C.sub.5 -alkenyl or C.sub.5 -C.sub.7 -cycloalkyl; phenyl which may be substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -dialkylamino, acetylamino, fluorine, chlorine or bromine;

R.sup.5 is hydrogen; chlorine;

C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkanoylamino, which may have C.sub.1 -C.sub.4 -alkoxy, phenoxy or chlorine as substituents, C.sub.2 -C.sub.3 -alkenoylamino, benzoylamino, ureido, mono- or di-C.sub.1 -C.sub.4 -alkylureido or C.sub.1 -C.sub.4 -alkylsulfonylamino;

R.sup.6 is hydrogen, chlorine, C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkoxy;

R.sup.7 is hydrogen, C.sub.1 -C.sub.8 -alkyl or phenyl;

R.sup.8 is hydrogen, C.sub.1 -C.sub.8 -alkyl, which may have phenyl, furyl or thienyl as substituents, C.sub.5 -C.sub.7 -cycloalkyl or phenyl.

3. A process for transferring an azo dye by diffusion from a transfer to a plastic-coated substrate with the aid of a heat source, which comprises using for this purpose of transfer on which there is or are situated one or more azo dyes of the formula I ##STR36## in which the substituents have the following meanings: X is a radical of the formula IIb ##STR37## where R.sup.2 is hydrogen, C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, chlorine or bromine, and

K is the radical of a coupling component III

H--K III

of an aniline, aminoaphthaline, pyrazole, diaminopyridine, hydroxypyridone or tetrahydroquinoline.

4. A process as claimed in claim 3, wherein K is of:

aniline derivatives of formula IIIa ##STR38## aminoaphthaline derivatives of the formula IIIb ##STR39## pyrazole derivatives of the formula IIIc ##STR40## diaminopyridine derivatives of the formula IIId ##STR41## hydroxypyridone derivatives of the formula IIIe ##STR42## tetrahydroquinoline derivatives of the formula IIIf ##STR43## wherein R.sup.3, R.sup.3', R.sup.4 and R.sup.4' are each hydrogen; C.sub.1 -C.sub.10 -alkyl whose carbon chain may be interrupted by from one to three oxygen atoms in ether function and which may bear the following substituents: cyano, hydroxyl, phenyl, phenoxy, phenylaminocarbonyloxy, benzyloxy, benzoyloxy, which may have C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, fluorine, chlorine or bromine as substituents, C.sub.1 -C.sub.4 -alkanoyloxy, C.sub.1 -C.sub.8 -alkoxycarbonyloxy, C.sub.1 -C.sub.8 -alkoxycarbonyl, mono- or di-C.sub.1 -C.sub.8 -alkylaminocarbonyloxy, in the last three of which the carbon chain may be interrupted by one or two oxygen atoms in ether function;

C.sub.3 -C.sub.5 -alkenyl or C.sub.5 -C.sub.7 -cycloalkyl; phenyl which may be substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -dialkylamino, acetylamino, fluorine, chlorine or bromine;

R.sup.5 is hydrogen; chlorine;

C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkanoylamino, which may have C.sub.1 -C.sub.4 -alkoxy, phenoxy or chlorine as substituents, C.sub.2 -C.sub.3 -alkenoylamino, benzoylamino, ureido, mono- or di-C.sub.1 -C.sub.4 -alkylureido or C.sub.1 -C.sub.4 -alkylsulfonylamino;

R.sup.6 is hydrogen, chlorine, C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkoxy;

R.sup.7 is hydrogen, C.sub.1 -C.sub.8 -alkyl or phenyl;

R.sup.8 is hydrogen, C.sub.1 -C.sub.8 -alkyl, which may have phenyl, furyl or thienyl as substituents, C.sub.5 -C.sub.7 -cycloalkyl or phenyl.

5. A process as claimed in claim 1, wherein the heat source is a thermal printing head.

6. A process as claimed in claim 3, wherein the heat source is a thermal printing head.